Line output functions require coordinates in logical units, which GDI uses to draw a line in logical space. (The use of logical units ensures device independence in Windows.) GDI maps this line from the logical space to pixels on the device. The number of logical units that GDI maps to a pixel depends on the current mapping mode. When GDI draws a line, it excludes the last specified point.
If an application draws lines and does not create a new pen, GDI uses the default pen. This pen is black and is one pixel wide when the mapping mode is MM_TEXT. An application can create a new pen of a different width, style, and color by using the CreatePen function. The new color is dependent on the color capabilities of the output device. The new style can be solid, dotted, dashed, or combined (dotted and dashed). Once an application creates a new pen, it can select the pen into a display context by using the SelectObject function.